(1) Field of the Invention
The present invention relates to a joined article, a process for producing said joined article, and a brazing agent for use in producing such a joined article.
(2) Related Art of the Invention
Since aluminum nitride has high heat conductivity, high electric insulation property, low thermal expansion, a low dielectric constant, etc., aluminum nitride has been widely used in various ways, for example, as a substrate material for high output semiconductor elements. In particular, various constructions of joined articles composed of aluminum nitride members and ceramic members and joined articles composed of aluminum nitride members and metallic members have been used in various ways. For example, as to ceramic heaters, electrostatic chucks, high frequency electrodes, etc. to be used in the semiconductor producing apparatuses, joining needs to be effected between aluminum nitride members and various ceramic members, between aluminum nitride members and tools for setting thermocouples, between aluminum nitride members and electrodes.
In order to join a ceramic member to a metallic member, it has been heretofore known that a brazing material is interposed between the ceramic member and the metallic member, and both the members are joined together by melting the brazing material under heating. However, although a number of brazing materials are known for metals, any of those brazing materials has poor wetting upon type ceramic members, particularly made of non-oxide type ceramic materials. Among them, it was difficult to firmly join the aluminum nitride member to the metallic member by brazing.
Under the circumstances, as a brazing material for joining a non-oxide type ceramic member to a metallic member or the like is used a brazing material containing an active metal such as titanium or zirconium for improving wettability of the brazing material. For example, according to "Joining between aluminum nitride and metals" (Yoshikuni NAKAO, "Light metal welding" vol. 31, 1993, No. 8, pp 359-365), it is known that various alloys including Ag--Cu based alloys and Ag--Cu--Ti based alloys have been tested as brazing materials for joining aluminum nitride to copper, and that titanium, zirconium, niobium, hafnium or vanadium is incorporated into the brazing materials made of the above alloys. Each of these active metals locally exists near the surfaces of the aluminum nitride members in such a manner that a reactive layer is formed in a thickness of a few to several .mu.m.
However, the reaction layer composed of such an active metal may be converted to a brittle intermetallic compound with the result that joining strength decreases. In particular, the present inventors found out that the above active metals have not necessary sufficient corrosion resistance.
Specifically, a halogen based corrosive gas is used as an etching gas, a cleaning gas or the like in a semiconductor producing apparatus. The present inventors found out that when joined articles were produced by joining aluminum nitride members to metallic members by using various metallic brazing materials mentioned above, and the resulting joined articles were subjected to a test for exposing them to such a halogen based corrosive gas, the joined articles were rapidly corroded with the halogen based corrosive gas. As a result, since the gas is likely to leak from the joined interface of the joined article, such a joined article cannot be used in a situation in which gas tightness is is required. Further, joining strength of some joined articles remarkably dropped. Therefore, a brazing material is demanded, which can be favorably used as a brazing material for ceramic members and has improved wettability upon ceramics, particularly, non-oxide type ceramic materials, and possesses especially high corrosion resistance.